Structured grids like Cartesian or stratigraphic grids are state-of-the-art for three dimensional modeling of the subsurface and a set of advanced visualization and modeling tools are available for these types of grids. However, tetrahedral meshes are becoming more and more important for geo-modeling applications since they can conform to complex geometries and provide more flexibility in terms of mesh resolution. Therefore, techniques for visualizing and modeling tetrahedral meshes need to be developed. Geological models are rich in information of different nature like topology of fault blocks, geological properties, geophysical data (e.g. seismic), stratigraphic layers or distances to geological interfaces like faults or to artifacts (e.g. wells). For an optimal interpretation, these layers of information can be combined into a single image using multi-texture capabilities of modern graphics hardware. An image consists of a set of user-defined iso-value surfaces and crosssections. Boolean operations of Constructive Solid Geometry with constant complexity are directly performed on the graphics hardware and allow complex geological and geometrical conditional queries. The computation and rendering of the iso-value surfaces is performed in real time on models with up to several hundred thousand cells on normal consumer hardware.